Semiconductor device capable of high-voltage operation

ABSTRACT

A semiconductor device capable of high-voltage operation includes a semiconductor substrate, a first well region, a second well region, a first gate structure, a first doped region, a second doped region, and a second gate structure. The first well region is formed in a portion of the semiconductor substrate. The second well region is formed in a portion of the first well region. The first gate structure is formed over a portion of the second well region and a portion of the first well region. The first doped region is formed in a portion of the second well region. The second doped region is formed in a portion of the first well region. The second gate structure is formed over a portion of the first gate structure, a portion of the first well region, and a portion of the second doped region.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 62/306,661 filed Mar. 11, 2016, the entirety of which is incorporated by reference herein.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to integrated circuits (ICs), and in particular to semiconductor devices capable of high-voltage operation and methods for forming the same.

Description of the Related Art

Recently, as demand has increased for high-voltage devices such as power semiconductor devices, there has been an increasing interest in research on high-voltage metal-oxide-semiconductor field effect transistors (HV MOSFETs) applied in high-voltage devices.

Among the various types of high-voltage metal-oxide-semiconductor field effect transistors (HV MOSFETs), semiconductor devices such as lateral double diffused metal-oxide-semiconductor (LDMOS) devices are often used.

However, with progress being made in semiconductor fabrication, the breakdown voltage of high-voltage MOSFETs for high-voltage devices needs to be increased further. Thus, a reliable high-voltage MOSFET for high-voltage devices having an increased breakdown voltage is needed to meet device performance requirements as the needs in semiconductor fabrication of high-voltage devices continue.

BRIEF SUMMARY OF THE INVENTION

An exemplary semiconductor device comprises a semiconductor substrate, a first well region, a second well region, a first gate structure, a first doped region, a second doped region, and a second gate structure. The semiconductor substrate has a first conductivity type, and the first well region formed is in a portion of the semiconductor substrate, having a second conductivity type that is the opposite of the first conductivity type. The second well region is formed in a portion of the first well region, having the first conductivity type. The first gate structure is formed over a portion of the second well region and a portion of the first well region. The first doped region is formed in a portion of the second well region, having the second conductivity type. The second doped region is formed in a portion of the first well region, having the second conductivity type. The second gate structure is formed over a portion of the first gate structure, a portion of the first well region, and a portion of the second doped region.

An exemplary method for forming a semiconductor device comprises providing a semiconductor structure comprising a first gate structure, a first well region, and a second doped region, and forming a second gate structure over a portion of the first gate structure, a portion of the first well region, and a portion of the second doped region. The semiconductor structure further comprises a semiconductor substrate, a second well region, a first gate structure, and a first doped region. The semiconductor substrate has a first conductivity type, and the first well region is formed in a portion of the semiconductor substrate, having a second conductivity type that is the opposite of the first conductivity type. The second well region is formed in a portion of the first well region, having the first conductivity type. The first doped region is formed in a portion of the second well region, having the second conductivity type. The second doped region is formed in a portion of the first well region, having the second conductivity type. The first gate structure is formed over a portion of the second well region and a portion of the first well region.

Another exemplary method for forming a semiconductor device comprises providing a semiconductor structure comprising a first gate structure, a first well region, and a second doped region in a first region, and an isolation element in a second region, and simultaneously forming a second gate structure over a portion of the first gate structure, a portion of the first well region, and a portion of the second doped region in the first region, and a third gate structure over a portion of the isolation element in the second region. The semiconductor structure further comprises a semiconductor substrate, a second well region, a first gate structure, and a first doped region. The semiconductor substrate has a first conductivity type, and the first well region is formed in a portion of the semiconductor substrate in the first region, having a second conductivity type that is the opposite of the first conductivity type. The second well region is formed in a portion of the first well region, having the first conductivity type. The first doped region is formed in a portion of the second well region, having the second conductivity type. The second doped region is formed in a portion of the first well region, having the second conductivity type. The first gate structure is formed over a portion of the second well region and a portion of the first well region. The isolation element is formed in a portion of the semiconductor substrate in a second region that is different from the first region. The third conductive layer is formed over the isolation element.

A detailed description is given in the following embodiments with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:

FIG. 1 is schematic cross section showing an intermediate stage of a method for forming a semiconductor device according to an embodiment of the invention;

FIG. 2 is schematic cross section showing an intermediate stage of a method for forming a semiconductor device according to an embodiment of the invention;

FIG. 3 is schematic cross section showing an intermediate stage of a method for forming a semiconductor device according to an embodiment of the invention;

FIG. 4 is schematic cross section showing an intermediate stage of a method for forming a semiconductor device according to an embodiment of the invention;

FIG. 5 is schematic cross section showing an intermediate stage of a method for forming a semiconductor device according to an embodiment of the invention; and

FIG. 6 is schematic cross section showing an intermediate stage of a method for forming a semiconductor device according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims.

FIGS. 1-6 are schematic cross sections showing a method for forming a semiconductor device according to an embodiment of the invention, respectively showing an intermediate stage of the method. The semiconductor device formed by the method shown in FIGS. 1-6 comprises a high-voltage metal-oxide-semiconductor field effect transistor (HV MOSFET) capable of high-voltage (e.g. 100 volts or above) operations.

In FIG. 1, a substantially fabricated semiconductor structure is provided. As shown in FIG. 1, the semiconductor structure is provided with two different regions A and B. Region B can be adjacent to region A or separated from region A by another region (not shown) formed therebetween.

As shown in FIG. 1, the semiconductor structure in region A comprises a semiconductor substrate 100 such as a silicon substrate. The semiconductor substrate 100 may have a first conductivity type such as P-type. An isolation element 108 is respectively disposed in opposite end portions of the substrate 100 in region A. The isolation elements 108 can be the shallow trench isolation (STI) elements shown in FIG. 1, but are not limited thereto. In some embodiments, the isolation elements 108 can be field oxide (FOX) isolation elements. The isolation elements 108 may comprise insulating materials such as silicon oxides, but they are not limited thereto. A deep well region 102 is formed in a portion of the semiconductor substrate 100 underlying the isolation elements 108. The deep well region 102 may have a second conductive type that is the opposite of the first conductivity type, for example N-type. Moreover, a well region 104 is formed between the deep well region 102 and each of the isolation elements 108. A well region 106 is formed in a portion of the semiconductor substrate between the well regions 104, and is above the deep well region 102. The well regions 104 and the well region 106 may have the first conductivity type, for example P-type. A well region 110 is formed in the semiconductor substrate 100 between the isolation elements 108, the well region 106 and the well regions 104. The well region 110 may have the second conductive type, for example N-type. A well region 112 is formed in a portion of the well region 110 and is adjacent to the one isolation element 108. The well region 112 may have the first conductivity type, for example P type. A doped region 114 is formed in a portion of the well region 112, and may have the second conductivity type, for example N-type. Another doped region 116 is formed in a portion of the well region 110, and is adjacent to the right isolation element 108. The doped region 116 may have the second conductivity type, for example N-type. The doped regions 114 and 116 may have a doping concentration greater than that of the well region 110.

In region A, a gate structure G1 is formed over a portion of the well region 112 and a portion of the well region 110, comprising a dielectric layer 118 and a conductive layer 120 formed over the dielectric layer 118. In one embodiment, in region A, the gate dielectric layer 118 may comprise silicon oxide, silicon nitride or the like, and may have a thickness of about 23-140 Å. The conductive layer 120 may comprise conductive materials such as polysilicon, metal or the like, and may have a thickness of about 800-2000 Å.

In addition, the semiconductor structure in region B further comprises another isolation element 108 formed in a portion of the substrate 100. Another gate structure G2 is formed over a portion of the isolation element 108, comprising the dielectric layer 118 and the conductive layer 120. In one embodiment, in region B, the gate dielectric layer 118 may comprise silicon oxide, silicon nitride or the like, and may have a thickness of about 23-140 Å. The conductive layer 120 may comprise conductive materials such as polysilicon, metal or the like, and may have a thickness of about 800-2000 Å.

In FIG. 2, a dielectric layer 122 is conformably formed over the semiconductor structure shown in both regions A and B shown in FIG. 1, covering the top surface of the semiconductor substrate 100 and exposed surfaces of the gate structures formed one the semiconductor substrate 100. In one embodiment, the dielectric layer 122 may comprise silicon oxide, silicon nitride or the like, and may have a thickness of about 200-1200 Å. The dielectric layer 122 may be thicker than the dielectric layer 118.

In FIG. 3, a conductive layer 124 is conformably formed over the semiconductor structure in both regions A and B shown in FIG. 2, covering the top surface of the dielectric layer 122. In one embodiment, the conductive layer 124 may comprise conductive materials such as polysilicon, metal or the like, and may have a thickness of about 300-2000 Å. The conductive layer 124 may be thicker than the conductive layer 120.

In FIG. 4, patterned mask layers 126 a and 126 b are respectively formed over a portion of conductive layer 124 (see FIG. 3) in regions A and B, and an etching process 128 is performed to remove the portion of the conductive layer 124 not covered by the patterned mask layer 126 a and 126 b. As shown in FIG. 4, the patterned mask layer 126 a and 126 b may comprise material such as photoresists or the like, and the etching process 128 can be, for example, a dry etching process. The etching process 128 stops on the dielectric layer 122, thereby forming a patterned conductive layer 124 a in region A and a patterned conductive layer 124 b in region B. The patterned conductive layer 124 a in region A is formed over a portion of the gate structure in region A and a portion of the semiconductor substrate 100 adjacent to the gate structure, and the patterned conductive layer 124 b in region B is formed over a portion of the gate structure but is not over the semiconductor substrate 100.

In FIG. 5, another etching process 129 is performed next to remove the portion of the dielectric layer 122 (see FIG. 4) not covered by the patterned mask layer 126 a and 126 b, and the patterned conductive layer 124 a and 124 b. The etching process 129 can be, for example, a dry etching process. As shown in FIG. 5, the etching process 129 stops on the conductive layer 120 and the substrate 100, thereby respectively forming a patterned dielectric layer 122 a in region A and a patterned dielectric layer 122 b in region B. The patterned dielectric layer 122 a in region A is formed under the patterned conductive layer 122 a and over a portion of the gate structure in region A and a portion of the semiconductor substrate 100 adjacent to the gate structure, and the patterned dielectric layer 122 b is formed under the patterned conductive layer 124 b in region B and is formed over a portion of the gate structure but is not over the semiconductor substrate 100.

In FIG. 6, after removal the patterned mask layers 126 a and 126 b shown in FIG. 5, another gate structure G3 comprising the patterned conductive layer 124 a and the patterned dielectric layer 122 a is formed in region A, covering a portion of about 20%-80% of a top surface of the underlying gate structure G1 comprising the conductive layer 120 and the dielectric layer 118. In addition, yet another gate structure G4 comprising the patterned conductive layer 124 b and the patterned dielectric layer 122 b is formed in region B, covering a portion of about 70%-90% of a top surface of the underlying gate structure G2 comprising the conductive layer 120 and the dielectric layer 118.

As shown in FIG. 6, in region A, the gate structure G3 comprising the patterned conductive layer 124 a and the patterned dielectric layer 122 a, and the gate structure G1 comprising the conductive layer 120 and the dielectric layer 118 may be combined to function as a combined gate of a semiconductor device capable of high-voltage operations, and the doped region 114 and the doped region 116 may function as source and drain regions, respectively. Through the use of the combined gate shown in FIG. 6, a more uniform electrical field contribution can be observed in the portion of the well region 110 underlying the combined gate during operations of the semiconductor device shown in FIG. 6 when compared with another semiconductor device that is similar to the one shown in FIG. 6, but which comprises only the gate structure G1 comprising a conductive layer 120 and a dielectric layer 118 and a dielectric layer 122. Accordingly, the semiconductor device capable of high-voltage operation shown in FIG. 6 can operate at a higher voltage of about 9-100 volts, which is about 100-1100% higher than a semiconductor device that is similar to the one shown in FIG. 6, but which comprises only the gate structure G1 comprising a conductive layer 120 and a dielectric layer 118 and a dielectric layer 122.

Moreover, in region B shown in FIG. 6, the conductive layer 124 b, the dielectric layer 122 b and the conductive layer 120 form an additional capacitor which can be simultaneously formed during formation of the semiconductor device capable of high-voltage operations shown in region A of FIG. 6.

As shown in FIG. 6, for the ease of illustrating the electrical potential provided to the combined gate in region A and the capacitor in region B, conductive contacts 128 a, 128 b, 128 c and 128 d, and conductive lines 130 a, 130 b, and 130 c can be further provided to the semiconductor structure. In region A, the conductive contact 128 a is connected to the conductive layer 120 and the conductive contact 128 b is connected to the conductive layer 124 a, and the conductive contacts 128 a and 128 b are both connected the conductive line 130 a, so that the gate structure G3 comprising the patterned conductive layer 124 a and the patterned dielectric layer 122 a and the gate structure G1 comprising the conductive layer 120 and the dielectric layer 118 may be provided with the same electrical potential during operations. In addition, in region B, the conductive layer 124 b is connected to the conductive contact 128 c and the conductive line 130 b, and the conductive layer 120 is connected to the conductive contact 128 d and the conductive line 130 c. The conductive lines 130 b and 130 c may be provided with different electrical potentials during operations, so that a capacitor can be formed by the conductive layers 124 b and 120 and the dielectric layer 122. In one embodiment, the conductive contacts 128 a, 128 b, 128 c and 128 d may comprise conductive materials such as tungsten, copper or the like, and conductive lines 130 a, 130 b, and 130 c may comprise materials such as tungsten, copper or the like.

While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements. 

What is claimed is:
 1. A semiconductor device, comprising: a semiconductor substrate having a first conductivity type; a first well region formed in a portion of the semiconductor substrate, having a second conductivity type that is the opposite of the first conductivity type; a second well region formed in a portion of the first well region, having the first conductivity type; a first gate structure formed over a portion of the second well region and a portion of the first well region, wherein a first dielectric layer of the first gate structure has a constant thickness; a first doped region formed in a portion of the second well region, having the second conductivity type; and a second doped region formed in a portion of the first well region, having the second conductivity type; and a second gate structure formed over a portion of the first gate structure, a portion of the first well region, and a portion of the second doped region.
 2. The semiconductor device as claimed in claim 1, wherein the first gate structure comprises a first conductive layer formed over the first dielectric layer, and the second gate structure comprises a second dielectric layer and a second conductive layer formed over the second dielectric layer.
 3. The semiconductor device as claimed in claim 2, further comprising: an isolation element disposed in a portion of the semiconductor substrate; a third conductive layer formed over the isolation element; a third dielectric layer formed over the third conductive layer; and a fourth conductive layer formed over the third dielectric layer.
 4. The semiconductor device as claimed in claim 3, wherein the third conductive layer, the third dielectric layer, and the fourth conductive layer form a capacitor.
 5. The semiconductor device as claimed in claim 3, wherein the third conductive layer and the second conductive layer are formed simultaneously.
 6. The semiconductor device as claimed in claim 3, wherein the third dielectric layer and the second dielectric layer are formed simultaneously.
 7. The semiconductor device as claimed in claim 3, wherein the fourth conductive layer and the second conductive layer are formed simultaneously.
 8. The semiconductor device as claimed in claim 3, wherein the first conductivity type is P-type and the second conductivity type is N-type.
 9. The semiconductor device as claimed in claim 3, wherein the first dielectric layer has a thickness of about 23-140 Å, and the second and third dielectric layers have a thickness of about 200-1200 Å.
 10. The semiconductor device as claimed in claim 3, wherein the second gate structure covers about 20%-80% of a top surface of the first gate structure.
 11. The semiconductor device as claimed in claim 3, wherein second conductive layer comprises polysilicon or metal.
 12. A method for forming a semiconductor device, comprising: providing a semiconductor structure comprising: a semiconductor substrate having a first conductivity type; a first well region formed in a portion of the semiconductor substrate, having a second conductivity type that is the opposite of the first conductivity type; a second well region formed in a portion of the first well region, having the first conductivity type; a first doped region formed in a portion of the second well region, having the second conductivity type; a second doped region formed in a portion of the first well region, having the second conductivity type; and a first gate structure formed over a portion of the second well region and a portion of the first well region, wherein a first dielectric layer of the first gate structure has a constant thickness; and forming a second gate structure over a portion of the first gate structure, a portion of the first well region, and a portion of the second doped region.
 13. The method as claimed in claim 12, wherein the first gate structure comprises a first conductive layer formed over the first dielectric layer, and the second gate structure comprises a second dielectric layer and a second conductive layer formed over the second dielectric layer.
 14. The method as claimed in claim 13, wherein the first dielectric layer has a thickness of about 23-140 Å, and the second dielectric layer has a thickness of about 200-1200 Å.
 15. The method as claimed in claim 12, wherein the second gate structure covers about 20%-80% of a top surface the first gate structure.
 16. The method as claimed in claim 13, wherein the second conductive layer comprises polysilicon or metal. 